An injecting machine uses a large pressure to inject material plastic in a mold. Therefore, the locking force of the mold must be greater than the injecting pressure of the injecting machine. Otherwise, the plastic material can be pushed out of the mold, making the products have undesirable hairy sides.
A conventional mold locking device, as shown in FIG. 4, includes a support disc 10, a movable disc 20, and connecting rods 30 with joints are provided between the movable disc 20 and the support disc 10. A hydraulic oil cylinder 40 is mounted on the front of the support disc 10. A cross-shaped head 50 is connected with a piston rod of the oil cylinder 40 for pushing the movable disc along the guide rods 60 to lock a mold disposed between the movable disc 20 and a stationary disc 70.
The conventional mold locking device just mentioned has undesirable features, such as (1) the bearings in the connecting rods are easily worn out, deteriorating the accuracy of the machine, and (2) the pushing distance for locking is too short to adjust the thickness of the mold.
Another conventional mold locking device utilizes an oil cylinder to directly lock a mold. But, for that system, related components are many, and are inconvenient for performing repair work.